Masking means and cleaning techniques for surfaces of substrates

ABSTRACT

The invention relates to apparatus for use in the coating of surfaces of substrates by Physical Vapor Deposition systems (PVD) wherein the deposition in material is applied onto the said surfaces by the sputtering of the same using the PVD system. The invention provides means for preventing sputtering material from applying or landing onto surfaces other than which is desired to be coated in the said coating process. The masking means allow the prevention and/or removal of such material which is known as backscattered material and the invention described claims protection for several embodiments and methods of achieving this thereby improving subsequent adhesion propertied and optical quantities, if applicable, of the coating.

The invention relates to the provision of masking means for certainsurfaces of substrates when other surfaces of the said substrates arecoated by a Physical Vapour Deposition system (PVD) wherein thedeposition of material is applied by sputtering of the material onto thesurfaces to be coated.

In particular the invention relates to improvements in the applicationof coatings to substrates such as optical lenses and other articles ofsimilar dimensions. The lenses can be used for many purposes, includinguse in spectacle frames, and may be formed from glass or a plasticsmaterial.

In any sputtering process there is a prevalence of material moving ontoand around the surface of the substrate which is being coated. Although,as in the coating process described in our clients co-pendingapplication PCT/GB92/00071, considerable control of the sputteringprocess can be achieved to obtain the best possible coating finish onthe coated surface it has been found that it is not possible tocompletely control the path of the sputtered material.

To briefly describe a sputtering coating process and with reference tothe applicants' machine and apparatus described in their co-pendingapplication, there is typically provided a plurality of substrates, inthis case lenses, mounted in lens holders and received in a disc holderwhich in this embodiment is held in a horizontal plane in a chamber. Inproximity to the disc there is provided at least one magnetron andtarget, the target containing the material which it is desired besputtered onto the lens, typically as an oxide, and the magnetroninduces sputtering of the material when the chamber is in vacuum.Typically the machine is preprogrammed such that after the lens holdershave been placed on the disc the machine is operable to apply a first"adhesion" layer of material and then at least one coating of thedesired material oxide onto a surface of each of the lenses byactivating sputtering of the target as the disc holder is rotated. Thesputtering of the material is then followed by rotating the disc andsubstrates through a reactive plasma from an unbalanced magnetron whichencourages a chemical reaction such as oxidation to occur in thematerial to arrive at the desired coating on the surface. In the case ofthe applicant's machine and other, similar machines, there is providedmeans for coating both optical surfaces of the lens wherein when thefirst surface of the lens is coated, the lens is turned over and thesecond surface is coated.

While this and sputter deposition machines in general have been found tobe of commercial value it has been found that problems exist with theoccurence of sputtered material landing on the second surface of thelens during sputter coating of the first surface of the lens, and viceversa. This is known as back-scattering and can cause problems once thefirst surface has been coated and, if required, the lens is turned overto perform the coating of the second surface of the lens. In the eventof the second surface being required to be coated an adhesion layer isapplied thereto and this layer will, in some instances, not adhere tothe surface due to the irregularities caused by the backscatteredmaterial which has been applied therein during the coating of the firstsurface.

Furthermore, it has been found that the lenses which are affected by thebackscattering problem can subsequently be rejected after a period oftime due to inferior optical quality. The reduction in optical qualityoccurs over a period of time after substantial use of the lens as partof, for example, to spectacles where loss of the coating can occur andaccelerated lifetime tests have shown that coating loss and poor opticalquality occur on the second surface which has been subjected toback-scattering.

While the problem can exist with the coating of any lens it has beenfound to be particularly prevalent when lenses are mounted in positionin the apparatus for coating of the surfaces and a gap exists betweenthe second surface of the lens and the lens holder. The gap can be aslittle as 0.5 mm but typically a gap of more than 1 mm has been found tocause these problems. Lenses which are particularly prone to theseproblems are cut lenses or a lens to correct astigmatism but in generalany lens can be affected, even if it is an uncut lens and the surfacefirst coated is convex, can leave a gap through which back-scatteredmaterial can pass to deposit on the second surface of the lens duringcoating of the first surface.

The aim of the present invention is to provide a masking means so thatthe second surface of a substrate, such as a lens, is protected fromreceiving backscattered material during the sputtering of material tocoat a first surface of the substrate. A further aim is to provide ameans for masking the second surface of the lens in such a manner thatthe masking can be applied and removed quickly and to also provide ameans for removing any backscattered material from said second surface.

The present invention relates to a masking means for use with apparatusfor the coating of at least one surface of a substrate by sputterdeposition of material thereon, and wherein prior to coating a firstsurface of said substrate by sputter deposition the said masking meansand/or substrate are brought into at least partial contact to mask atleast a second surface of the substrate from the deposition of materialthereon.

Typically the substrate which is coated is a lens having two opticalsurfaces, a first and a second optical surface, and wherein during thecoating of the first surface by sputter deposition the second surface isin contact with the masking means thereby preventing the same fromreceiving any sputtered material thereon.

In one embodiment the masking means is an adhesive membrane which isapplied to the second surface prior to the coating of the first surfaceand then removed from the second surface to allow the coating of thesame if required. Typically said membrane is in the form of an adhesivetape and said adhesive is of a type to be removable from the lenswithout leaving an adhesive deposition thereon. A known tape is soldunder the name "Surface Saver".

In a further embodiment the masking means is a release agent which isapplied to the second surface to mask the same and is easily removableupon completion of the sputtering process for coating the first surface.

One typical release agent is provided in a gel or pressurised particlespray which is applied by spraying or by any other appropriate methodonto the second surface to mask the same during sputtering.

A third embodiment of the masking means is a layer of material uponwhich the substrate is placed, said layer insertable in, or an integralpart of, the substrate holder of the sputter deposition apparatus.Typically, when the lens is in place in the holder, the layer serves toat least partially contact the second surface of the lens to protectsame from back-scattered material during sputtering.

The layer is preferably formed of a material which is sufficientlydeformable to allow variation in the substrate dimensions and type to betaken into account. In one preferred embodiment the layer is formed ofneoprene material which takes the shape of the substrate surface placedthereon. Alternatively the layer is a foam material but in whichevermaterial, the layer is provided in a form such that the same is part of,or as an insert into, the substrate holder, such that when the substrateis fitted into the holder, the layer is deformed to contact at least theperipheral edge of the second surface thereby masking the surface fromany back-scattering which may occur. The layer can further be shaped tomatch the shape of the surface itself hence providing contact with themajority of the second surface.

When the substrates to be coated are standard cut sizes a furtherembodiment is to provide a substrate holder in the form of a cullotte,said cullotte including location means for said substrates and formedsuch that when the substrates are put in position the apertures aresealed and hence no sputtered material can pass through to the secondsurface which is not being coated hence preventing back scattering.

Preferably at each location means there is provided a lip, which neednot be deformable, said lip arranged to lie adjacent to, or in contactwith, the edges of the substrate, when the same is placed in thecullotte location means thereby ensuring an improved seal between thecullotte and the substrate.

In an alternative embodiment and when the apparatus is used for coatingof substrates of different sizes, the lips are movably mounted such thatthe same can be moved to contact with the edges of the substrate.

Typically the sputter deposition apparatus is PVD apparatus comprisingat least one sputter magnetron for the reactive sputtering of materialonto the first surfaces of the substrates and a reaction zone wherein aplasma, glow discharge, ion source or other reaction means causes areaction to occur in the sputter deposited material to form the requiredcoating composition.

The invention also provides a method for the coating by PVD of anoptical surface of a lens comprising the steps of;

placing the lens in a holder such that a first surface to be coated isexposed to the sputter deposition apparatus;

applying a masking means to a second surface of the lens to preventsputter deposition of material thereon;

activating the sputter deposition apparatus to provide an adhesion layerand the required coating to the first surface; removing the lens fromthe holder; and

exposing the second surface of the lens by removing the same from themasking means.

In one embodiment when both the first and second surfaces are to becoated the method includes the further steps of placing the lens in aholder with the second surface exposed to the sputter apparatus,operating the sputter apparatus to deposit an adhesion layer and therequired coating material on the second surface.

In a further aspect of the invention there is provided apparatus for thecoating of surfaces of substrates by sputter deposition of materialthereon, said apparatus provided for the coating of at least a firstsurface of said substrates and wherein the apparatus includes means forthe removal of material deposited on any surfaces other than said firstsurface, by any of chemical etching, plasma treatment or furthersputtering by ion bombardment.

In one embodiment the apparatus includes an ion source and sputteringfrom the ion source onto the surfaces of the substrate is used to cleanthe back-scattered material to leave a regular surface for theapplication of an adhesion layer and subsequent coatings thereon. Thesputtering is preferably provided as an integral part of the coatingprocess.

The method for cleaning surfaces of backscattered material comprises thestep of applying a coating by sputter deposition to a first surface of asubstrate, such as a lens having two surfaces to be coated, held in aholder, removing the lens from the holder, exposing the second surfaceto the sputter apparatus and operating the sputter apparatus in acleaning mode to remove backscattered material on said second surface.

A specific embodiment of the invention will now be described withreference to the accompanying drawings wherein;

FIG. 1 illustrates a conventional disc and lens holder;

FIG. 2 illustrates a lens being held in a holder;

FIG. 3 illustrates the sputtering of a first surface of the lens indiagrammatic form;

FIG. 4 illustrates a cross section of a lens holder with the secondsurface masked according to one embodiment of the invention;

FIG. 5 illustrates a cross section of a lens holder and a lens with amasking means according to a second embodiment of the invention;

FIG. 6 illustrates a cross section of a lens holder and a lens with amasking means according to a third embodiment of the invention; and

FIG. 7 illustrates a cross section of a lens holder and masking means ina further embodiment of the invention.

Referring firstly to FIG. 1 there is illustrated a disc 2 which isdisposed for rotation about a central axis 4. Provided around theperiphery of the disc are a series of indents of similar dimension.Provided adjacent to the disc in a magazine 8 are a plurality of lensholders 10 each of which carries a lens 12 as shown in FIG. 2. Duringoperation of the machine, within which the disc and the lens holdersshown are located, holders are picked up by the disc to fill all theindents 6 available following which the disc is rotated and the lensheld thereon coated by sputtered material from sputter depositionapparatus and reaction means past which the substrates are repeatedlyrotated.

FIG. 2 illustrates the lens holder 10 in greater detail and the holderincludes a lower flange 14 upon which the lens sits during coating. Thelens can be shaped and in this case consists of a concave surface 16 anda convex surface 18. FIG. 3 illustrates the sputtering of the firstsurface 16 of the invention which in this case is the concave surface ofthe lens but which may equally be the convex surface if required, by thedeposition of material 20 thereon to form a coating 21 thereon. Thedepth of coating and the number of types of coating can be altered tosuit requirements and the actual apparatus and control methods aredisclosed in greater detail in the co pending application referred toearlier in the specification.

Although attempts are made to control the path of the sputtered material20 it has been found that there is still opportunity for material to bedeposited on areas which are not required to be coated as shown by thematerial 22. This is known as back-scattering and FIG. 3 clearly showshow this back-scattering can lead to the deposition of material on thesecond surface 18 of the lens. This makes any subsequent coating of thesecond surface 18 very difficult, due to the reduction in adhesion ofthe adhesion layer to the lens surface caused by the back-scatteredmaterial.

FIG. 4 illustrates one method of overcoming this problem wherein thesecond surface 18 is masked from any backscattering by the applicationof a protective layer 24 prior to the sputtering process. This layer canbe any of an adhesive membrane, a release agent or a gel like materialbut in any case is easily removable upon the completion of sputtering.

FIG. 5 illustrates an alternative embodiment for masking the secondsurface of the lens during sputtering wherein the lens holder 10 isprovided with a layer of deformable material 26 in the form of a shapedfoam layer. The foam layer may comprise a foam based plastics material.As shown, the layer is of sufficient size such that when the lens is infitted position it causes the foam 26 to deform 28 and hence seal thesecond surface from damage from back-scattering.

FIG. 6 illustrates a further embodiment wherein the holder 10 includes alayer 30 of neoprene material onto which the lens is placed. The layer30 adapts in form to match the form of the second surface of the lensand thus the same is masked from backscattered material. A furtherembodiment as in FIG. 7 is particularly useful when the depositionapparatus is for use to coat a lens and is provided with a cullotte 34to carry lenses of standard sizes which typically are uncut stock lenseswhich tend to come in standard diameters e.g. 65 mm, 70 mm, 75 mm, 80mm. The cullotte includes a plurality of apertures for the reception oflocation means 35 for the lenses 37 and preferably adjacent eachlocation there is provided a lip 36 which is designed to engage with thelens edges to prevent backscattered material from entering the protectedsurface. When the lenses are in position for coating there is no way forthe sputtered material to pass through to the surface which is not beingcoated, therefore no apertures are present in the cullotte and hence theoccurrence of back scattering is prevented.

By utilising any of the masking methods so described the second surfaceof the lens can be protected during coating of the first surface bysputtering. By protecting the second surface the user reduces theopportunity for optical defects of the second surface to occur and, ifthe second surface is required to be coated, ensures that there will beno deposition thereon to effect the adhesion of said second coating.

As an alternative to the above masking means, as part of the automaticlens coating process of the sputter deposition apparatus, a stage isincluded in the coating process for the specific purpose of removing anyback-scattered material from the second surface prior to the coating ofsaid second surface. Such removal is in one embodiment, achieved by thedirecting of sputtered material from, for example, an ion sourceincluded as part of the apparatus onto the second surface. Thesputtering of said ion source will cause any back-scattered material onthe second surface to be removed and in this embodiment there is theadded advantage that no masking of the second surface is required.

The sputter removal of the backscattered material can be achieved usingeither inert gas ion bombardment or by using reactive ion etching usinga chemically active gas species. In reactive ion sputtering the removaloperation works by converting the surface backscattered material into avolatile gaseous compound thereby removing the same. In sputter cleaningusing inert gas ion bombardment the backscattered material is physicallyremoved by the impact of energetic inert gas ions. Sputter removaloccurs when the ion source energy exceeds the sputtering threshold of 40eV. The efficiency of the process is improved as the ion energy isincreased although substrate damage also increases with increasing ionenergy. The optimum ion energy for this process is in the region 80 eVto 200 eV.

Whichever embodiment is used it has clearly been identified thatback-scattering of material onto a surface which is subsequently to becoated creates problems during the actual coating of that surface andcan cause adhesion problems during use of the lens. The invention ofthis application provides solutions to this problem which eliminate theopportunity for backscattered material to cause defects in the coatingof lens surfaces.

What is claimed is:
 1. A method for preventing the backscattereddeposition of at least one sputter material onto a first surface of atleast one substrate having a plurality of surfaces during the coating ofa second surface of the substrate when placed in a carrier adapted formovement within a vacuum chamber with the at least one sputter materialby a sputter deposition apparatus, comprising the steps of:sealing thefirst surface of the at least one substrate while exposing the secondsurface of the at least one substrate; said sealing of the first surfaceincludes contacting in a sealing engagement a first sealing area with anadhesive material or release agent to mask the first surface, said firstsealing area being selected from the group consisting of: at least aperiphery of said first surface, a peripheral edge of said substrate,and at least a periphery of said first surface and a peripheral edge ofsaid at least one substrate; activating the sputter deposition apparatusin said vacuum chamber, thereby sputtering the at least one sputtermaterial toward the at least one substrate and coating the secondsurface of the at least one substrate with the at least one sputtermaterial; unsealing the first surface of the at least one substrate,whereby the second surface is coated with the at least one sputtermaterial and the first surface is substantially devoid of the at leastone sputter material; activating the sputter deposition apparatus,thereby sputtering the at least one sputter material toward the at leastone substrate and coating the first surface of the at least onesubstrate with the sputtered material, whereby the second surface andthe first surface are sequentially coated.
 2. The method according toclaim 1 further comprising:sealing the second surface of the at leastone substrate while exposing the first surface of the at least onesubstrate to the at least one sputter material; and said sealing of thesecond surface includes contacting in a sealing engagement a secondsealing area with a masking material to mask said second surface, saidsecond sealing area being selected from the group consisting of: atleast a periphery of said second surface, a peripheral edge of saidsubstrate, and at least a periphery of said second surface and aperipheral edge of said substrate.
 3. The method according to claim 2further comprising sealing the second surface of the at least onesubstrate before exposing the first surface of the at least onesubstrate to the at least one sputter material.
 4. The method accordingto claim 2 further comprising coating the first surface with arespective sputter material which is different from the sputter materialcoating the second surface.
 5. The method according to claim 1 furthercomprising placing the at least one substrate in a substrate holderwherein one of the first or second surfaces is exposed to the at leastone sputter material and wherein one of said first or second surfaces ismasked.
 6. The method according to claim 1 further comprising causing areaction to occur in the sputtered material.
 7. The method according toclaim 6 further comprising initiating said reaction by a plasma reactionmeans, a glow discharge reaction means, or an ion source reaction means.8. The method according to claim 6 further comprising producing saidreaction by one of a plasma reaction means, a glow discharge reactionmeans, and an ion source reaction means.
 9. The method according toclaim 1 wherein said adhesive material further comprises a removableadhesive tape.
 10. The method according to claim 1 wherein said releaseagent is a material selected from the group consisting of gel andpressurized particle foam.
 11. The method according to claim 1 furthercomprising providing a support layer, wherein the at least one substraterests upon the support layer during the coating of the second surface.12. The method according to claim 11 further comprising contacting atleast the peripheral edge of the first surface of the at least onesubstrate with said support layer.
 13. The method according to claim 11further comprising a substrate holder wherein said support layer isintegral with said substrate holder.
 14. The method according to claim11 further comprising removably engaging said support layer with asubstrate holder.
 15. The method according to claim 11 wherein saidsupport layer is made from a deformable material.
 16. The methodaccording to claim 18 wherein said deformable material is a materialselected from the group consisting of neoprene and a foam-based plasticsmaterial.
 17. The method according to claim 1 furthercomprising:providing a plurality of substrate locating means, whereineach locating means is adapted to hold a respective substrate, andwherein each substrate locating means has at least one lip for engagingan edge of the respective substrate; and providing a substrate receivingmeans for receiving said plurality of substrate locating means.
 18. Themethod according to claim 1 wherein the at least one substrate is anoptical lens.
 19. The method according to claim 18 wherein the opticallens comprises at least one concave surface.
 20. The method according toclaim 18 wherein the optical lens comprises at least one convex surface.21. The method according to claim 1 wherein at least one of said firstand second surfaces is curved.
 22. The method according to claim 21wherein at least one of said first and second surfaces is concave. 23.The method according to claim 21 wherein at least one of said first andsecond surfaces is convex.
 24. A sputter deposition system for coatingat least one surface of at least one substrate by sputter deposition,said system comprising:a holder for mounting said at least one substratein a vacuum chamber; at least one sputtering device for sputtering amaterial onto said at least one surface of said at least one substrateexposed to said sputtering device; wherein said at least one substratewhen mounted in said holder has an exposed surface and a masked surfaceopposing said exposed surface which is exposed to said sputtering deviceand at least one of said exposed and masked surface has a shape selectedfrom the group consisting of concave, convex, and concave and convex;means for masking said masked surface of said at least one substrate andpreventing the deposition of said sputtered material onto said maskedsurface; and said masking means being adapted in relation to said atleast one substrate to contact at least a peripheral edge of saidsubstrate and thereby prevent the deposit of sputtered material onto thesurface which is masked; wherein said masking means is an adhesivemembrane.
 25. A system according to claim 24 wherein said at least onesubstrate is a plurality of substrates and said masking means isprovided for each of said plurality of substrates placed in said vacuumchamber.
 26. A system to claim 24 wherein said adhesive membrane is areleasable adhesive tape.
 27. A system according to claim 24 including ameans for creating a reaction zone within the vacuum chamber.
 28. Asystem according to claim 27 wherein said means for creating saidreaction zone is selected from the group consisting of a plasma creatingmeans, a glow discharge and an ion source.
 29. A system according toclaim 28 wherein at least two magnetrons are provided having differenttarget materials to allow a multilayered coating to be applied to the atleast one substrate.
 30. A system according to claim 24 said at leastone substrate is an optical lens.
 31. A system according to claim 24wherein said at least one sputtering device is a magnetron including atarget of a selected material to be deposited on said exposed surface ofsaid at least one substrate.
 32. A sputter deposition system for coatingat least one surface of at least one substrate by sputter deposition,said system comprising:a holder for mounting said at least one substratein a vacuum chamber; at least one sputtering device for sputtering amaterial onto said at least one surface of said at least one substrateexposed to said sputtering device; wherein said at least one substratewhen mounted in said holder has an exposed surface and a masked surfaceopposing said exposed surface which is exposed to said sputtering deviceand at least one of said exposed and masked surface has a shape selectedfrom the group consisting of concave, convex, and concave and convex;means for masking said masked surface of said at least one substrate andpreventing the deposition of said sputtered material onto said maskedsurface; and said masking means being adapted in relation to said atleast one substrate to contact at least a peripheral edge of saidsubstrate and thereby prevent the deposit of sputtered material onto thesurface which is masked; wherein said masking means is a release agent.33. A system according to claim 32 wherein said release agent is a gelor pressurized particle foam applicable by spraying.
 34. A sputterdeposition system for coating at least one surface of at least one bysputter deposition, said system comprising:a holder for mounting said atleast one substrate in a vacuum chamber; at least one sputtering devicefor sputtering a material onto said at least one surface of said atleast one substrate exposed to said sputtering device; wherein said atleast one substrate when mounted in said holder has an exposed surfaceand a masked surface opposing said exposed surface which is exposed tosaid sputtering device and at least one of said exposed and maskedsurfaces has a shape selected from the group consisting of concave,convex, and concave and convex; means for masking said masked surface ofsaid substrate and preventing the deposition of said sputtered materialonto said masked surface; and said masking means being adapted inrelation to said at least one substrate to contact at least a peripheraledge of said substrate and thereby prevent the deposit of sputteredmaterial onto the surface which is masked; wherein said masking means isa layer of material onto which a seal area contacts, said seal area isof the group consisting of: at least a periphery of the said maskedsurface; a peripheral edge of said at least one substrate; and at leasta periphery of the said masked surface and a peripheral edge of said atleast one substrate.
 35. A system according to claim 34 wherein saidmaterial layer is provided as an integral part of said holder.
 36. Asystem according to claim 35 wherein said material layer is a deformablematerial.
 37. A system according to claim 34 wherein said material layeracts as said holder and said system includes a plurality of said holdersmounted on a carrier provided in said vacuum chamber.
 38. A systemaccording to claim 37 wherein said material layer is a deformablematerial.
 39. A system according to claim 37 wherein said carrierincludes a plurality of location means for receiving a plurality ofsubstrates therein.
 40. A system according to claim 39 characterized inthat each location means includes a lip around the periphery thereofwhich contacts with a contact area and said lip acts as a means to maskthe opposing surface of the at least one substrate from the depositionof sputtered material thereon, said contact area is of the groupconsisting of:the periphery of the said opposing surface; the edge ofthe at least one substrate mounted thereon; and the periphery of thesaid opposing surface and the edge of the at least one substrate mountedthereon.
 41. A system according to claim 34 wherein said material layeris a deformable material.
 42. A system according to claim 41 whereinsaid deformable material is selected from the group consisting ofneoprene and a foam based plastics material.
 43. A method for coating asurface of each of a plurality of substrates, each having at least asurface having a shape selected from the group consisting of concave,convex and concave and convex, said method comprising the stepsof:placing said substrates in a carrier adapted for movement in a vacuumchamber; operating at least one sputter deposition device in said vacuumchamber to apply a sputtered material to an exposed surface of each ofsaid substrates; masking a masked surface opposing said exposed surfaceof each of said substrates prior to operation of the sputtering device;and said masking includes contacting a masking area with a masking meansto mask said surface, said masking area is of the group consisting of:at least a periphery of said masked surface, a peripheral edge of saidsubstrate, and at least a periphery of said masked surface and aperipheral edge of said substrate; such that when said sputtering deviceis operated said masking means simultaneously prevents the deposition ofsaid sputtered material onto said masked surface of each of saidsubstrates; wherein said masking includes applying said masking means tosaid substrates prior to said substrates being placed onto said carrierfor said vacuum chamber and said masking means is in the form of any ofan adhesive membrane or release agent.
 44. A method according to claim43 including the step of providing a means for creating a reaction ofsaid sputtered material on said substrates.
 45. A method according toclaim 43 wherein said placing includes mounting each substrate on asubstrate holder and said substrate holders are mounted on the carrierfor the vacuum chamber.
 46. A method according to any of the precedingclaims 44-45 wherein when the coating of the exposed surface of each ofthe substrates is complete the substrates are removed from the carrierin the vacuum chamber and then replaced on the same such that thepreviously opposing masked, surfaces of the substrates are exposed forcoating by the sputter deposition of material thereon.
 47. A methodaccording to claim 46 wherein the previously exposed coated surface ofeach of the substrates are masked by bringing the same into contact withthe masking means such that a coated area is contacted with the maskingmeans, said coated area is of the group consisting of:at least theperiphery, edge of the surface, and at least the periphery and edge ofthe surface.